Strain

(1 syl.). To strain courtesy. To stand upon ceremony.
Here, strain is to stretch, as parchment is strained on a drum-head.
When strain means to filter, the idea is pressing or squeezing through
a canvas or woollen bag.

Strain at a gnat and swallow a camel.

To make much fuss about little pecadillos, but commit offences of
real magnitude. “Strain at” is strain out or off (Greek, di-ulizo). The allusion is to the practice of filtering wine for
fear of swallowing an insect, which was “unclean.” Tyndale has “strain
out” in his version. Our expression “strain at” is a corruption of
strain-ut, “ut” being the Saxon form of out, retained in the words
ut-most, utter, uttermost, etc.

The quality of mercy is not strained

(Merchant of Venice, iv. 1)- constrained or forced, but
cometh down freely as the rain, which is God's gift.